Mechanical Response and Damage Behavior of Asphalt Pavements with Variable Structural Configurations

This study evaluated the influence of crushed aggregate subbase stiffness and thickness on flexible pavement performance. Two pavement configurations were evaluated under dual-wheel loading to assess surface deformation, fatigue and rutting damage, and depth-dependent stress–strain responses. The results indicated that increasing SB2 elastic modulus improved load distribution and reduced surface vertical displacement in both configurations, with the five-layer system consistently exhibiting lower surface deformation due to improved stiffness gradation. However, responses at the bottom of the asphalt layer were configuration-dependent: increasing SB2 stiffness reduced tensile strain and fatigue damage in the four-layer system but increased fatigue demand in the five-layer system because of strain redistribution near the asphalt-base interface. At the top of the subgrade, both systems exhibited identical stiffness-dependent response trends, while the five-layer configuration primarily reduced response magnitudes. Quantitative damage analysis demonstrated that the five-layer system achieved 40–55% lower fatigue damage and up to 85% lower rutting damage compared to the four-layer system, whereas increasing subbase thickness provided a secondary but consistent benefit. Overall, fatigue cracking controlled pavement performance, highlighting the dominant role of pavement configuration over subbase stiffness.